The invention relates generally to wet chemistry processing systems and methods and, more particularly, to batch processing systems and methods that are utilized in conjunction with semiconductor wafers.
Mechanized transfer systems used in industrial multi-stage wet chemistry processes generally fall into one of two categories: (1) in-line processing, and (2) batch processing. Since the present invention relates primarily to batch processing, various prior-art batch processing systems and methods will now be considered. The systems used in batch processing are divided into two sub-categories: (i) mass transfer mechanisms, and (ii) free ranging hoist mechanisms. By way of introduction, the principles involved in each of the two aforementioned categories will now be described, and the disadvantages of each category will be set forth in greater detail.
Although the principles of the present invention may be applied to many industries and many mechanized transfer processes within these industries, an ophthalmic lens multi-stage critical cleaning system preceding a vacuum will be discussed for purposes of illustration.
A. Mass Transfer Technique:
Using a single hoist or walking beam, batches of substrates (in this example, lenses), racked in carrier baskets, are simultaneously transferred from one position (for example, fluid tank) to another position from an initial load position through washing, rinsing, and drying stages. Finally, batches of the substrates are transferred to an unload position, where the carriers of clean and dry lenses are then transferred by hand or conveyor, to the next desired processing location. The next location could implement, for example, a vacuum coating or dip coating process.
Since all workloads in the line-up of process tanks are transferred simultaneously in the mass transfer method, transfer is fast and a maximum number of workloads (carriers of lenses) are processed in a given time period. However, this technique also presents a number of disadvantages. The time that workloads must remain in each process position is the same for all positions. The workloads cannot be processed for different times in each position. This can be a serious handicap for many process requirements, since different times are frequently required at different stages of the process. Instead, the processes themselvesxe2x80x94ultrasonic power, chemistry, temperature, etc., have to be adjusted until all positions require the same processing time. Another disadvantage is that the center-to-center distance between consecutive processing stages must be uniform. Yet another disadvantage is that the processing sequence must be truly sequentialxe2x80x94in other words, this technique has no ability to skip any processing stage.
B. Free Ranging Transfer Hoist Technique:
A free ranging transfer hoist is an electronically programmed transfer hoist with the capability of moving freely in both horizontal and vertical axes. The hoist transfers workloads from tank to tank, one workload at a time, and at differing time intervals, as required for each processing stage. This technique is advantageous in that it offers a flexibility of motion approximating that of a human operator. The free-ranging hoist is able to transfer workloads forward or backward to any desired processing stage, and to comply with whatever process time and transfer requirements each particular stage demands. Moreover, the physical spacing between the centerlines of sequential stages need not be identical. The free-ranging hoist is able to address spacing variations as dictated by differences in design of the various processing stages.
The free ranging transfer hoist technique presents a number of shortcomings. Transfer of workloads, one at a time, is very time-consuming. For process sequences involving a number of stages, a single transfer hoist is not able to keep up with the number of transfers required for a given processing cycle. When, due to a large number of processing positions, or limitations in travel speed, or short processing time requirements, or a combination of these factors, the travel time becomes equal to or larger than the process time, then the transfer system itself becomes the throughput-limiting factor (the bottleneck) in the system. The use of multiple robots, with an attendant increase in system cost, then becomes necessary.
For simple wet chemistry processing systems having few stages and not more than one kind of recipe or processing sequence, such as simple cleaning systems or low throughput systems, one of the two prior art work transfer systems described in the foregoing paragraphs may be quite adequate. However, for more complex processing requirements, or for applications requiring higher throughput capability, the compromises involved in prior art methods creates significant difficulties.
A primary object of the present invention is to provide a mass transfer system that offers the simultaneous transfer and time-saving efficiencies of prior art mass transfer techniques, while also offering some or all of the flexibility of prior-art free ranging hoist techniques. This object is achieved by equipping a mass transfer mechanism and an associated software control mechanism with the ability to retract a plurality of lifting arms (6), in a manner so as to select which of the processing stages (2) the lifting arms (6) will address for each transfer step, while omitting those steps for which transfer is not yet required. Thus, for example, a carrier basket (1) (also commonly referred to as a xe2x80x9cworkloadxe2x80x9d) may be moved from a spray-rinsing tank after only thirty seconds, to make room for another workload, while carrier baskets (1) in some other positions may not be transferred for several more minutes. The end result of this novel technique is that the overall throughput efficiency of the prior art mass transfer method is preserved, while the capabilities of the free ranging hoist to address various and multiple processing steps or recipes is accommodated.